Methods of the type indicated above are known from the prior art. They are used for the operation of the image-processing device, which handles the transmission of the image signal between the transmitter and the receiver. The transmitter is connected to, for example, a recording device or a data-acquisition device, by means of which the image signal is acquired. The image signal consists of a timed sequence of images, which contain the image content recorded by the recording device.
The transmission between the transmitter and the receiver proceeds in an exclusively digital manner, wherein compression can be carried out if desired. If the image signal is compressed before transmission, preferably a loss-free compression method is used. Alternatively, however, a lossy compression method could also be used. The transmission takes place preferably over a transmission route consisting of a shielded cable or comprising an optical fiber. It is obvious, however, that the transmission route can be designed in any suitable way.
When the image signal is transmitted in analog form, any problem with the transmission route has a visible effect on the transmission quality, so that, when the image signal displayed on the display device is observed, an essentially reliable judgment can be made about whether or not the image transmission process has been successful or faulty. When the images are transmitted in digital form, however, the problem can occur that, even though the transmission route is severely compromised, the images can still be displayed in a manner which appears qualitatively unimpaired, such as when, for example, one of the successive images is repeated. This is the case especially when an image buffer is assigned to the receiver, from which one of the most recent successfully transmitted images can be reproduced again. When this happens, a static or “frozen” image results, which does not represent the current image content.
The method indicated above is used in particular for imaging systems in the medical area. In these systems, it is very important to know whether or not the image being shown at any particular moment on the display device is current, that is, whether it comprises the current image content acquired by the recording device, or whether the image reproduction chain has frozen as a result of, for example, a fault in the image transmission process. If, for example, a patient is being treated on the basis of the displayed image, and if the person performing the treatment assumes that the displayed image is current whereas in fact it is frozen and no longer current, the consequences can be serious, and in particular the patient can suffer injury.